This invention relates to a method for taking an impression of a selected area in an internal bore of a tubular member and is especially adapted to take such an impression where the selected area of the bore is remote and in a hostile environment, such as in a string of production or drilling risers used in offshore drilling and production or in casing or tubing within the well itself, whether subsea or onshore.
In the drilling and production of oil and gas wells, there has been a long existing need for inspecting the internal bore of tubular members for broken threads, cracks, holes, scored seal surfaces, or perhaps an incorrectly threaded joint between two members, without returning the member or members to the surface of the water, in the case of a subsea well, or to the land in the case of an onshore well. Heretofore, such an inspection under such adverse conditions was virtually impossible. High water pressure, the remoteness of the area from the operator, vertical surfaces and their condition are but a few of the problems involved in such an inspection. As a result, many hours, days, and often weeks were spent fishing for obstacles or retrieving whole strings of tubular members because of an unidentified or incorrectly identified problem.
In addition, it is apparent that for such an inspection to be made under such adverse conditions, the device must be insensitive to ambient pressure, it must be capable of being operated remotely, whatever medium is used to make the impression, it must be capable of being separated from the member being examined, and it must not contaminate the member nor should the fluid and chemicals used react with the medium or with the member being examined. Also, the member and device must be capable of retrieval out of the bore of the member being inspected.
There are a number of prior art tools to take an impression of a bore, such as shown in the U.S. Pat. No. 3,916,871, where an elastically hardenable casting plastic is cast into a plug between inflatable dams. See also U.S. Pat. Nos. 3,862,047 and 3,978,398 which utilize a mixture such as rubber with magnetic particles as a recording medium.
However, none of the prior art patented devices provide a method capable of meeting the demands imposed on the device by such adverse conditions.